Feature Ultrasonic Phased Arrays Quickly Detect Corrosion The technology can be used on most common geometries, such as pipes, vessels, and tank bottoms suspected of having corrosion problems Industrial plants require safe and reliable operations, but corrosion is a major problem for the owners of industrial equipment, installations, and plants, due to the presence of corrosive chemicals and harsh operating and environmental conditions. For industries throughout the world, corrosion costs billions of dollars. Mitigation costs include corrosion prevention and detection, as well as repairing the results of corrosion. Corrosion requires reliable methods for efficient detection. If undetected for a long time, corrosion can cause leaks and component failures, which reduce the performance and reliability of important equipment. In extreme cases, corrosion can lead to unexpected disruptions that are often costly in terms of lost production, the expense of repairs, lost or contaminated products, environmental damage, and potential harm to humans. In many facilities, key equipment may have been in service for decades and have the potential to be compromised even by relatively slow corrosion mechanisms. What Is Corrosion? Corrosion in welds occurs despite the proper material having been selected, industry standards followed, and welds deposited that possess complete joint penetration and have the proper shape and contour. Corrosion occurs as a result of the material’s exposure to harsh conditions, and this may be external, internal, or both. Corrosion is a chemical or electrochemical reaction between a material, usually a metal, and its environment, which produces a deterioration of the material and its properties. Corrosion can be widespread and relatively uniform or localized, in the form of pitting and cracking. Considerable efforts are expended to reduce the extent of corrosion by techniques such as inhibitors, coatings, metallurgy selection, and cathodic protection. However, these methods are typically slow, and fail to completely prevent corrosion. It is, therefore, essential to continuously monitor critical equipment to prevent catastrophic failure and to maintain excellent onstream factors. How Can We Detect Corrosion? Usually, corrosion detection is performed with a thickness gauge or a portable flaw detector. The residual thickness is checked by spot measurements or a couple of coarse scans. If only general corrosion is present, this method works fine. However, this technique has a high chance of missing localized pitting corrosion, even when large surface samples are scanned. Ultrasonic Phased Array Ultrasonic phased array technology has become an established method for advanced nondestructive examination (NDE) applications. Phased array technology reveals defects hidden inside a structure or weld by testing the structural integrity. This newer ultrasonic testing technique is based on generating and receiving ultrasounds, but instead of a single transducer and beam, phased array equipment uses multiple ultrasonic elements and electronic time delays to create beams with constructive and destructive interference patterns — Fig. 1. Phased array is an advanced pulseecho technique that utilizes multiple miniaturized transducers and time delays to shape the ultrasonic beam to a desired angle and focus. The versatility of the system permits simultaneous views of different presentations, such as sectoral views as Fig. 1 — The latest phased array equipment, such as the Phasor CV/DM from GE Sensing & Inspection Technologies, uses multiple ultrasonic elements and electronic time delays. Advantages include repeatability, speed of inspection, and capability for inspecting complex geometries. Shown is the screen shot of the reference block. Inspection Trends / Winter 2011 27
Inspection Trends - January 2011 - Winter
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